Foundation anchor for floating marine platform

ABSTRACT

THE INVENTION RELATES TO A SEPARABLE COMPONENT FOUNDATION ANCHOR ADAPTED FOR POSITIONING AN OFFSHORE FLOATING PLATFORM OR OTHER FLOATABLE VESSEL AT A DESIRED DEEP WATER WELL DRILLING SITE. THE ANCHOR INCLUDES A RELATIVELY HEAVY PILOT MEMBER AND A SUBMERGIBLE CASING OR BALLAST SECTION. THE ANCHOR FURTHER INCLUDES MEANS TO ENGAGE THE LOWER END OF THE OFFSHORE PLATFORM TO MINIMIZE MOVEMENT OF THE LATTER AT THE WATER&#39;&#39;S SURFACE. THE BALLAST SECTION COOPERATES WITH THE PILOT MEMBER, FUNCTIONING SEQUENTIALLY AS A TRANSPORT MEANS TO THE OFFSHORE SITE, AND AFTER BEING BALLASTED AND SUBMERGED SUPPLEMENTS THE WEIGHTED PILOT SECTION. SAID BALLAST SECTION FURTHER MAY HOLD A QUANTITY OF FLUIDS USED IN AN OIL DRILLING OR PRODUCING OPERATION SUCH AS DRILLING MUD, CURDE OIL AND THE LIKE WHEREBY TO MINIMIZE THE NEED FOR ADDITIONAL PLATFORM SPACE TO STORE SUCH MATERIALS.

G. E. MOTT Oct. 12, 1971 FOUNDATLON ANCHOR FOR FLOATING MARINE PLATFORM Filed Feb. 17, 1970 2 Sheets-Shoot 2 United States Patent Olfice 3,611,734 Patented Oct. 12, 1971 3,611,734 FOUNDATION ANCHOR FOR FLOATING MARINE PLATFORM George E. Mott, Metairie, La., assignor to Texaco Inc., New York, NY. Filed Feb. 17, 1970, Ser. No. 11,998 Int. Cl. B63b 35/44 US. Cl. 61-465 12 Claims ABSTRACT OF THE DISCLOSURE The invention relates to a separable component foundation anchor adapted for positioning an offshore floating platform or other floatable vessel at a desired deep water well drilling site. The anchor includes a relatively heavy pilot member and a submergible casing or ballast section. The anchor further includes means to engage the lower end of the offshore platform to minimize movement of the latter at the waters surface. The ballast section cooperates with the pilot member, functioning sequentially as a transport means to the offshore site, and after being ballasted and submerged supplements the Weighted pilot section. Said ballast section further may hold a quantity of fluids used in an oil drilling or producing operation such as drilling mud, crude oil and the like whereby to minimize the need for additional platform space to store such materials.

BACKGROUND OF THE INVENTION In the offshore exploration and drilling of wells for gas and crude oil, such operations are usually performed from a fixedly positioned platform or a floating vessel. In the instance of the platform, elongated support legs extend through the body of water, and are anchored to the floor thereof by piles or other suitable means. In the floating vessel type arrangement, the vessel is maintained at the waters surface by anchoring means extending to the ocean floor, or by an inbuilt dynamic mechanism such as lateral thrusters and the like which are controllably operated to position the vessel within a limited area during the drilling operation.

One form of drilling platform believed to be particularly desirable in deep water comprises a floating vessel or platform at the waters surface which is maintained in a relatively fixed location by a rigid tethering column which extends to the ocean floor. The lower end of the tethering structure is normally anchored at a single point thereby allowing the surface platform to oscillate Within a limited arc in response to wind and wave displacing forces.

To maintain a safe anchoring force in this type of arrangement, the anchor means must of necessity be efficient, and have adequate weight and bearing area to withstand lateral forces applied to both the floating vessel, and to the tethering structure. As a matter of practicality, the anchor is normally formed of concrete or other material embodying weight and bulk to provide the necessary down pull whereby to achieve the desired vessel stabilization function.

Such anchors, because of their weight, are awkard to handle at the waters surface. This applies not only to the fabrication of the anchor but also to transporting the unit to an offshore site and to controllably lowering the same to the ocean floor.

Because of the uncertainty attached to the productivity, in terms of obtainable petroleum products, from any particular drilling site, it is desirable that as much as possible of the drilling and producing equipment be reusable at an alternate site. In this respect, the previously mentioned vessel or platform and tethering structure are reusable merely by disconnecting one or both from the ocean floor and floating them to the desired site. Thereafter they can be repositioned in the manner followed at the previous site. However, in the instance of the anchor or positioning member, it is often difiicult and impractical to attempt salvaging operations.

It is therefore one of the objects of the invention to provide a deep water anchor adapted to stabilize a floating well drilling vessel at the waters surface. A further object is to provide a readily submergible and salvageable anchor adapted for reuse. A still further object is to provide a multi-component anchor, being self-supporting while at the waters surface and which is controllably buoyant whereby to facilitate its being transported and submerged. Still another object is to provide a multicomponent anchor Which is separable into discrete components whereby each component can be individually submerged to or raised from a resting place at the ocean floor.

A still further object is to provide an anchor, a portion of which can be used for under water liquid storage.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view shown in partial cross-section of the presently contemplated foundation anchor. FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1. FIGS. 3 to 6 inclusive illustrate the sequential steps fol lowed in installing the separable anchor in conjunction with the placing of an offshore marine platform. FIG. 7 illustrates a locking mechanism used to secure the pilot member to the ballast section of the anchor for transport to a job site and for securing the two units together at the ocean floor.

In overcoming the foregoing problems and toward achieving the stated objectives, there is disclosed a partially salvageable, multi-component foundation anchor for an olfshore drilling storage or other apparatus. The anchor includes at least two members so connected as to permit their separation while at the waters surface whereby each member can be sequentially lowered to the ocean floor.

The anchor includes a pilot member formed of concrete or a similar material to provide an initial anchoring base. Said member is further provided with outwardly projecting connector means for engaging the lower end of a floating platform, or other vessel through a rigid tethering structure pivotally connected to the anchor and extending therefrom, to the vessel.

The ballast or support section, preferably fabricated in the form of a series of closed tubular members, is adapted to securely anchor the pilot member, or alternately to supportably suspend the latter as it is being lowered through the water. The ballast section embodies a plurality of internal, discrete compartments connected to manifold means whereby the Weight and the buoyancy of said section can be adjusted. Means is also provided for storing a flowable fluid such as crude oil or drilling mud. In the instance of the drilling mud, the latter may also function as ballast to maintain the position of the ballastable section at the ocean floor.

Referring to the drawings FIG. 6 illustrates an anchor 10 of the type contemplated partially imbedded into the floor of a body of water. A marine platform 15 extends in a vertical direction from a point adjacent the ocean floor to a distance above the latters surface. A deck 16 is carried at the upper end of the platform, which may hold drilling equipment, producing equipment, ballasting equipment, instruments and the like. The platform includes a plurality of elongated legs or columns 17 having buoyancy tanks 18 in the upper end. In its normal operating position platform 15 extends substantially vertically in the body of water. The lower end of one or more of legs 17 separably engages coupling means carried on anchor 10. The platform can thus oscillate in a restrained manner in response to wind and water displacing forces about the fixed anchor position and yet remain relatively stable to permit continuous drilling producing or other operations from the deck 16.

The multi-component, though separable anchor includes in essence a controllably positioned pilot member 11 which is substantially surrounded by, and retained in contact with a ballastable casing section 12. The external configuration of the pilot member bears significant relevance only to the extent that the flat, pad-like configuration will facilitate its holding function by providing suflicient weight and adequate bearing area to prevent the anchor from sinking too deeply into a soft substratum.

Pilot member 11 comprises a relatively heavy reinforced slab or pad 13 cast of concrete. Said pilot member as shown, assumes a planar, pad-like configuration having opposed upper and lower surfaces 21 and 22 respectively. A primary reason dictating a generally flat disposition to this member is, as noted above, the desirability of providing an undersurface with a relatively broad bearing area for seating against a soft substratum without excessive sinking into the latter.

To assume a positive hold between foundation pad 13, and the substratum, undersurface 22 is provided with an enclosing lip 23 formed at the pad member periphery, thereby defining a shallow internal cavity 24. Lip 23 is provided with a downward or terminal edge having an abrupt or sharp corner to permit ease of entry of lip 23 when lowered onto a substratum surface.

At several locations around the periphery of pad 13 a beveled surface 60 and slot 61 are provided to receive shear pins 62 which are used to lock ballast section 12 to anchor weight 11. Shear pins 62 are in turn housed in hydraulic cylinders 63 which can be actuated by a pump 64 forcing hydraulic fluid from a reservoir 69, through lines 65, to cylinders 63. The pressurized fluid acts against pistons 64 which in turn compresses spring 66 and retracts pins 62. By releasing pressure on line 65, pins 62 are free to retract from the downward weight of ballast section 12. The hydraulic system is used to release weight section 11 from buoyant section 12 while both are floating at the surface of the water.

Pad 13 is further provided with transverse passages 19 which extend from the pad upper face to the lower face, thereby affording communication for mud and water between the internal cavity and the surrounding water as pad 13 is lowered onto a penetrable substratum.

Said pad member 13 is further provided with a coupling means adapted to operably engage a corresponding element of the leg 17 whereby to restrain lateral movement of platform with a limited degree. Said coupling means includes at least one, and preferably a plurality of upstanding coupling posts 27 spaced horizontally apart at the pad upper surface. Posts 27 are uniform in diameter, having the lower end firmly imbedded in the concrete pad body to fix the posts in a firm upright disposition.

The ballastable or casing section 12, comprises in essence one or more tanks interconnected to a pumping system adapted to vary the buoyancy of said section 12 whereby to permit the casing to optionally float at the waters surface, or to be submerged. Said casing 12 includes a plurality of hollow members 28, 29, 31 and 32, preferaby cylindrical in cross-section, which are disposed about the casing outer edge. Said hollow members are formed of heavy walled cylindrical tubing or pipe,

1 being end-welded one to the other to form a continuous ring-like arrangement. The arrangement utilized is dependent largely on the configuration of the pilot member pad 13 whereby the two engaging elements can be brought into close cooperation for transporting purposes or while in position on the ocean floor.

While the present arrangement of pad 13 and casing section 12 are shown as being rectangular the actual configuration utilized is dependent on a number of factors.

Each cylindrical member at the casing section is provided with one or more internal panels such as 33, disposed transversely of said member whereby to define a tank such as 34 and 36 adjacent said panels. To minimize the shifting of ballast fluid during movement or positioning of the ballastable section 12, said tanks 34 and 36 may be provided with transverse perforated baflies 37 and 38 Whereby movement of contained water or drilling mud is dampened. As shown in FIG. 2, ballastable section 12 cooperatively engages the peripheral seating edge 21 of foundation pad 13 along the contoured seat on the latter. Although casing section 12 is shown as overhanging the edge of the foundation pad 13, it is understood that such an arrangement is not essential since the casing can function as well were the latter to be disposed directly on top of the foundation pad.

Casing section 12 futrher includes transversely disposed structural cross braces 56 and 58 which extend between the opposed cylindrical sections. The cross bracing sections intersect a central main brace 39, and are provided with spaced apart intermediate guide rods 41 and 42 whereby to define a relatively limited guide opening 43 therebetween. The one or more guide openings are so arranged in the casing 12 to cooperatively register with and engage the respecting coupling posts 27 depending upwardly from the foundation pad.

The said casing section 12 further embodies pumping means connected to the respective tanks 34 and 36 within the casing. Said pumping means may either be located on platform 15 or be remotely controlled from the waters surface. Said pumping means includes for example a manifolding arrangement represented by upward extending line 44 which connects to a pump means 46 which is either disposed within the tank section 36 or on platform deck 16. The flow of material either ballasting water or drilling mud, is controlled through a series of valves represented by control valves 47 and 48, Said valves may either be located on platform deck 16 located on the bottom. In the latter case the valves would be remotely controlled from platform deck 16 or other surface vessel.

Thus when the casing section 12 functions as a transport vehicle for the entire assembled anchor 10, the easing and the foundation pad 13 are fixedly engaged at the waters surface. Preferably, foundation pad 13 is entirely submerged to minimize the buoyancy lift required of the casing 12. In such condition the unit can be towed at the surface of the water until reaching the place of submergence at the underwater well site.

The respective pilot member 11 and casing section 12 are connected by means whereby the respective parts can be readily separated to permit lowering of the foundation pad 13 to the ocean floor. Said connecting means can assume a number of different forms any of which are adapted to maintain the separable relationship thereof. For properly aligning the respective pilot member 11 and casing section 12 the latter are provided with one or more and preferably at least two flexible lines 51 and 52 such as cable or chain. The latter connect at their lower end to the foundation pad 13 prior to the pad being lowered to the ocean floor. The cables are retained at the waters surface and tension controlled as pad 13 is lowered and casing 12 remains floating. Thereafter, with the respective flexible lines registered in the guide means 43 on the casing section 12, the latters 'buoyancy is adjusted to controllably sink the unit into the water and be guided to its position in engagement with the foundation pad 13.

The connection system may include one or more cable wind-ups carried on the casing section 12 and provided with power winch means upon which the cable or chain is taken up. However, the cables may also be controlled by an external means such as a derrick barge or the like at the waters surface which maintains th disposition of casing 12 as the latter is lowered to its point of engagement in the ocean floor.

As shown in FIGS. 3 to 6, inclusive, the mode for installing an anchor of the type described, for use with the marine structure follows a sequence of steps. As noted herein, the anchor 10 is towed with the pilot member 11 and casing section 12 joined to the desired offshore location. Thereafter, the flexible guide lines 51 are connected to foundation pad 13 preferably at the upper end of the respective posts 27. The said guide lines are registered in the respective guide openings 43 on the casing 12, the foundation pad is then lowered to the ocean floor. The lowering operation is achieved by disconnecting the foundation pad 13 from the casing 12 and maintaining an orderly descent of the foundation pad either by the external derrick barge 54 or by controlling the speed of the respective support cables as they are unwound from the power winch on the casing.

As shown in FIG. 4, with foundation pad 13 at least partially imbedded in the ocean floor substratum, buoyancy tanks 34 and 36 are selectively flooded to alter the buoyancy characteristics of said casing. The upper ends of lines 51 are connected to buoys 57 at the surface for subsequent connection to platform 15. Section 12 is then controllably lowered to the ocean floor along the guide lines 51, whereby the respective guide openings 43 register with the upstanding posts 27.

Casing 12 can be provided with one or more piles 56 having the lower edge depending from the underside of the casing 12. Thus, as the latter achieves its resting position, the weight of the unit will cause the respective piles 56 to enter the substratum whereby to improve the ability of the anchor to maintain a fixed position against horizontal displacing forces.

With the anchor foundation 10 firmly in place, the guide lines 51 are passed through the respective legs 17 of the marine structure 15. By controllably altering the buoyancy characteristics of the latter, the lower end of said structure is guidably lowered to the ocean floor whereby the respective leg ends register with the upstanding posts 27 in the foundation pad 13.

At such time as it becomes desirable to move the equipment from one side to another a reverse procedure can be followed to salvage either or both the casing member 12 as well as the foundation pad 13.

Notably, platform 15 is floated to disengage from pad 13. The buoyancy of the casing 12 is next gradually altered such that the entire unit controllably rises to the surface of the water along the guide lines 51. Thereafter using the casing 12 as a surface support structure either alone or together with a derrick barge 5,4, foundation pad 13 can be dislodged from its resting place and lifted to the surface. Where the foundation pad 12 is imbedded to such an extent as to resist efforts to dislodge the same, it can be abandoned in favor of providing a similar pad adapted to engage casing 12, for the next installation at which the anchor is to function.

'With the casing 12 in the submerged position cooperatively connected to the foundation pad, the usual ballasting material is water. However, to more effectively utilize the storage capacity of the respective ballasting tanks 34 and 36, the latter can be provided in whole or in part with a fluid used in the drilling operations such as drilling mud or the like. Thus, the drilling mud is pumped in liquid phase into the respective storage tanks 34 and 36, and maintained there until such time as the mud is required for the drilling operation. Thereafter as the mud is drawn or pumped from the tanks, the resulting space can be filled with water or other material to maintain the negative buoyancy of the casing 12.

Toward facilitating this transfer of drilling fluid, each storage tank 34 and 36 may be provided with means for maintaining the mud in a solution or flowable suspension whereby to be suitably handled by the pumping and manifold system. Thus each of said storage tanks may include in effect, an agitating pump connected to have the suction side thereof submerged in the storedfluid, and being provided with one or more discharge nozzles which are redirected into the fluid whereby the latter are subjected to violent agitation and thus maintain its fluid status. Toward achieving the same result, each of said compartments can alternately be provided with a stirring mechanism such as a motor mounted stirrer disposed within the compartment and surface control whereby to set in mo tion the contained drilling mud prior to its being withdrawn from the tank.

Obviously, many modifications and variations of the invention, as hereinafter set forth, may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are in dicated in the appended claims.

I claim:

1. A foundation anchor for a floating marine structure disposed substantially uprightly in a body of water, which foundation anchor includes;

a base member having coupling means dependent therefrom for operably engaging a submerged end of said marine structure whereby to limit movement of the latter in said body of water,

a buoyant casing engaging said base member and adapted to be detachably separated therefrom,

a pumping system in said buoyant casing, being operable to controllably adjust the buoying capabilities thereof whereby to remotely regulate the attitude of said casing in said body of water, and

guide means connecting said respective base member with buoyant casing and being operable to lower said base member in said body of Water to the floor thereof when said base member is detached from the floating buoyant casing, and for further guiding said buoyant casing to re-engage the base member at said ocean floor when said casing is adjusted to a condition of negative buoyancy.

'2. In a foundation anchor as defined in claim 1 wherein said base member includes; a relatively flat pad having opposed upper and lower surfaces, the latter forming a bearing area for engaging the underwater substratum.

3. In a foundation anchor as defined in claim 2 wherein said relatively flat pad includes; at least one transverse opening formed therein communicating said upper and lower surfaces.

4. In a foundation anchor as defined in claim 2 wherein said relatively flat pad includes; an upstanding lip depending downwardly from said lower surface thereby defining a cavity at said lower surface.

5. In a foundation anchor as defined in claim 4 wherein said upstanding lip comprises; a substantially continuous member that extends about the periphery of said pad to form said cavity.

6 In a foundation anchor as defined in claim 2 wherein said pad includes; seating means on said upper surface adapted to register a corresponding surface of said buoyant casing whereby to fixedly position the latter with respect to said pad.

7. In a foundation anchor as defined in claim 1 wherein said buoyant casing includes; a plurality of discrete buoyancy tanks, and said pumping system being separably communicated with the respective tanks and operable to regulate the buoyant capabilities thereof.

8. In a foundation anchor as defined in claim 1 wherein said pumping system includes; pumping means communicated with said respective buoyancy tanks and means to remotely actuate said pumping means for regulating the tank buoyancy.

9. In a foundation anchor as defined in claim 1 wherein said guide means includes; a flexible line communicated with the respective casing and base member, said flexible line being extendable to maintain said connection between said base member as the latter is lowered to the ocean floor.

10. In a foundation anchor as defined in claim 9 wherein said flexible line includes; a wind-up carried on said casing being operable to regulate the flexible line length as said base member is separated from said casing and means on the latter adapted to slidably engage said flexible line whereby to direct said easing into engagement with said base member as said casing is controllably lowered to the ocean floor.

11. In a foundation anchor as defined in claim 7 including; conduit means communicating said buoyancy tanks with a source of a fluidized material.

12. In a foundation anchor as defined in claim 7 including; conduit means communicating said buoyancy tanks with a source of a fluidized material and agitating means in said buoyancy means being operable to fluidize said material for passage thereof through said conduit means.

UNITED References Cited STATES PATENTS Kirby 61-46.5 Christensen 6l46.5

Templeton 114-.5 DX Newcomb 6146.5 Tittle 6l69 X Chamberlin et a1. 6146.5 Manning 980 X Blenkarn 6l46.5

Vilain 6146.5

Horton 114-.5 D

US. Cl. X.R. 

